Is repeat until effective for unit movement?

I have a Part with a BodyGyro and a BodyVelocity for each unit. On the server side, I have this FollowPlayerScript for each unit.

(There's nothing wrong with this script, its just slow)

while player.Character do

    local char = player.Character;

    repeat wait()

	destination = char.HumanoidRootPart.Position
	
	unit.BodyGyro.CFrame 		= blah blah
	unit.BodyVelocity.Velocity       = blah blah move;	
    
    until (main.Position - destination).magnitude < 6
    
    	stop(destination);
    
    wait(.2);
    
end

I'm experiencing a lot of lag and inaccuracies when I get about 20 units. Is using 'repeat until' bad for performance? Should I be doing a RenderStepped instead?

Whats the best practices for mass unit movement? I really don't want to be moving the units on the client.

EDIT:

I'm going to make a coroutine instead of lots of scripts. Hopefully this helps

local thread = coroutine.create(function()
	while true do
		wait(.1)	
	end
end)
coroutine.resume(thread)